To reach the summit of Matiu/Somes Island Historic and Scientific Reserve—the 25 ha island in the middle of busy Wellington Harbour—it’s necessary to scramble over a couple of fences, walk across a paddock where several grazing sheep stop eating long enough to watch you pass, and zigzag your way up to where five concrete structures remain from a World War II anti-aircraft position. On a clear day it’s a great place for a picnic.
If you have kids with you, the first thing they’ll do is run around the remnant gun emplacements playing hide-and-seek. Second, they’ll start collecting chicken bones. Adults don’t notice the bones right off because they’re partially hidden by the vegetation, but once the youngsters alert you to the mass chicken grave, you see bones everywhere. In fact, they change how you feel about your sandwiches, and you begin to wish you’d brought a blanket to sit on. Queries from the kids about this poultry cemetery aren’t easily answered. And after learning about the island’s recent history at the visitor centre—it served as an animal quarantine station for over 100 years before being transferred to the Department of Conservation (DOC) in 1995—you start to imagine what carnage might have occurred on the spot you’re trying to enjoy.
The kids collect bones for a while and then return to their games, allowing the adults to enjoy the panoramic views again. But when you see David Moss, the DOC ranger, you casually ask about the chicken remains. He smiles gamely, a certain glint in his eye, and you sense he’s been asked the question once or twice before. He says the bones come from takeaways around greater Wellington. The southern black-backed gulls (Larus dominicanus) that live on Somes Island scavenge chicken pieces from rubbish bins and litter all over the region, swallow them, and then fly to the island to regurgitate their “catch” and eat the meat themselves or feed it to their young. After a meal, only the bones remain.
Somes Island has been home to a sizable colony of southern black-backed gulls only since the early 20th century. Evidence suggests that when European settlers first arrived, black-backed gulls were solitary nesters, albeit throughout the country, and that there were perhaps only 90–100 nesting pairs in the Wellington region as recently as the late 19th century.
Stories persist of Captain Cook’s crews shooting the rarely seen gulls for their valuable feathers. Adult birds display comely plumage—white head, body, tail and underwings contrast with a black back and above-wing area. The largest gull to breed in New Zealand, the southern black-backed has an average wingspread of over a metre. Handsome parents notwithstanding, the mottled clove-coloured juvenile of the species could pass as the frumpy offspring of the larger, less showy brown skua. Young gulls don’t acquire full adult breeding dress until their third winter, by which time they have undergone two moults. The dissimilarity in appearance of immature gulls and their elders prompted Maori to give fully grown birds one name—karoro—and juveniles another—ngoiro.
Southern black-backed gulls—commonly referred to in other parts of the world as kelp gulls—are generally considered to occur in two subspecies: L. d. dominicanus, found in South America, Australia and New Zealand, around numerous subantarctic islands and on the Antarctic Peninsula; and L. d. vetula, which breeds mainly in South Africa and Madagascar. The name comes from the Dominican order of friars who wore black and white habit. In recent years, some avian researchers have called for L. d. vetula (common name cape gull) to be considered a completely separate species. Still other researchers believe the list of subspecies should be expanded from two to five to account for variations between populations.
Whatever name(s) we give them, southern black-backed gulls boast one of the most extensive breeding ranges of any seabird; and because they are highly adaptable and generalist feeders, that range continues to expand. For example, southern black-backed gulls did not become established in Australia until the past half-century. Now they’re a common sight there along coasts and at refuse tips.
Although we think of black-backed gulls as seabirds, that isn’t the whole story. While they’re most common on the coast, some breed far inland near fresh water, even beside alpine lakes and glaciers. From Tongariro to the Takitimus, a smattering of black-backed gulls can be found throughout the high country, while they also roam widely over farmland and open ground.
New Zealand is thought to have one of the largest populations of southern black-backed gulls of any country, estimated at more than one million. While increased human activity and the introduction of exotic species have inflicted havoc on many native-bird populations, black-backed gulls have thrived. Open rubbish tips, sewage outlets and waste from fishing boats and meat-processing operations provide gulls with a bon vivant existence.
By the end of the last century, the adult black-back population in the Wellington region alone had swelled to 20,000. Most of the gulls there had also exchanged solitary for colonial nesting, including over 1000 breeding pairs on Somes Island. In wilder, more isolated areas pairs still nest individually, jealousy guarding their territory against all intruders, including other gulls.
The energy expended protecting a nest and searching for food is considerable.
Consequently, most solitary nesters raise only one nestling per breeding season. When they don’t need to compete for food, gulls may take to living in colonies, and an unlimited food supply can increase chick production from one a season to three. Colonies offer better protection from predators. The gulls adopt extensive vocal and physical warning behaviours to ward off an array of predators, including humans. However not all colony members are guaranteed protective immunity. Fledglings that have strayed or been startled away from their nests are vulnerable to attack by adults.
Along with most other native birds, the southern black-backed gull received partial protection under the Wildlife Act of 1953. But by 1970 it had proliferated across the country to such an extent that it was removed from the Act’s list of protected species, becoming one of New Zealand’s few native birds without legal protection. At the time, the gull’s new status drew praise from farmers, many of whom saw the species as a threat to their livelihood through predation of livestock and its propensity to carry disease.
Ken Weir, the chief Animal Quarantine Officer on Somes Island from 1934 to 1959, told a Radio New Zealand reporter in the 1950s: “They [gulls] give us a lot of trouble at lambing time, especially the newborn lambs. If you’re not there they’ll kill them. First of all they pick the eyes out, and of course you’ve either got to destroy the lamb or they destroy it for you.” Nevertheless, according to Wildlife Service records and correspondence, predation of livestock was not the primary motivation for the gull’s removal from the protected list. At the time, just how damaging gulls were to livestock was still in dispute. In a stern letter to Federated Farmers of New Zealand in 1981, then Director of Wildlife Services R.T. Adams wrote:
In 1967 during the course of a control operation on gulls at Napier Airport, officers of the Wildlife Service investigated complaints by the Maraekakaho branch of Federated Farmers who alleged thousands of dollars worth of damage caused by gulls that nested nearby on the Ngaruroro River. That investigation showed that a significant proportion of the ‘predation’ was in fact directed at animals that had died at birth, and this was confirmed by the farmers themselves at a well-attended public meeting.
The chief reason given for taking the bird out of the Act was its detrimental effect on other, “more desirable” bird species, including shags, terns and the New Zealand dotterel. Other birds were likely vulnerable as well. For instance, takahe chicks in the remote Murchison Mountains have been seen to cower when black-backed gulls fly overhead. Gulls have won few popularity contests with humans over the years, so perhaps it isn’t surprising that there were only three formal complaints about the bird’s removal from the Act—from the Southland Acclimatisation Society, the executive of the Royal Forest and Bird Protection Society and one individual.
Geoff Keey, Forest and Bird’s Biosecurity Awareness Officer, states: “Our stance continues to be, if it’s native it should be protected. We accept that on a case-by-case basis there are times when the control of one species is necessary to protect another, but only in dire situations.”
With regard to the conservation of native wildlife, Forest and Bird maintains that numerous other factors, such as mammalian predation, land use and introduced weeds, are of greater concern than gulls. Keey refers to a recent study by DOC that identifies mammalian predators such as ferrets, cats and hedgehogs as the top killers of native birds on certain riverbeds.
“That isn’t to say that black-backed gulls aren’t causing problems for native birds in certain places, but I think sometimes they’re the scapegoat. It is much easier to blame a gull colony for a drop in waders, for example, than to acknowledge that altering water flows on many of our braided rivers has destroyed habitat.”
DOC Biodiversity Officer Rob Stone agrees that gulls have sometimes been wrongly blamed for out-competing other native birds, but feels that on Somes Island the control programme that has been embarked upon will aid the return of other species. “No self-respecting fluttering shearwater’s going to nest near a large colony of black-backed gulls,” he asserts. “They are some of the most industrious opportunists around. If something is down, they attack.”
Elizabeth “Biz” Bell of Wildlife Management International Limited (WMIL) concurs. “We were involved in DOC’s extensive gull-control programme on Mana Island, located on the west coast north of Wellington. The island has historically been an important nesting area for white-fronted terns, oystercatchers and other seabirds. When we started work on the island we encountered several thousand pairs of breeding black-backed gulls, and the other seabirds [were] in decline. With the gull numbers there in check, the island now sustains various other bird populations and those populations are increasing.”
In the late 1980s, Katikati ornithologist and photographer Brian Chudleigh and his wife, Cushla, noticed that black-backed gulls were predating most of the eggs in a colony of white-fronted terns on shell banks near Bowentown. The following year the gulls completely wiped out 180 nests and a colony of about 50 red-billed gulls after winter storms had stripped most of the vegetation cover from the shell banks. At that time DOC didn’t want to know and told the Chudleighs the black-backed gulls were protected.
The Chudleighs also notified DOC of problems on Matakana Island, where black-backed gulls appeared to be attacking the nests of New Zealand dotterels. The couple began destroying gulls’ eggs at the north end of the island, where about 40 pairs were nesting. They also killed the chicks raised by seven pairs on the Bowentown shell banks after observing the damage they were continuing to inflict on the terns and red-billed gulls.
A couple of years later DOC began to worry about the apparent failure of New Zealand dotterel chicks to fledge on Matakana Island and set video cameras to monitor dotterel nests. Surprise, the cameras revealed that predation by black-backed gulls was the main cause of mortality among dotterel chicks. By then the gull population at the north end of Matakana Island was pushing 1000, while the total for the island was probably more than 3000 pairs, up from about 400 when the Chudleighs counted nests there in the early 1980s. The half-dozen or more open rubbish tips around Tauranga Harbour had fuelled the gulls’ increase. Besides rubbish they were eating eggs and chicks of both New Zealand and banded dotterels, the latter by now almost entirely absent as a breeding species around the harbour.
DOC decided it had to act and set out to poison the gulls, but the operation went awry. Instead of the gulls dropping dead out of sight on Matakana Island, they died all round the harbour, upsetting many people. A second attempt proved more successful, and there are now no black-backed gulls nesting on Matakana Island, though some still nest around Tauranga—a few even on roofs—and there have been attacks on passers-by.
Dotterels have since made a huge comeback on Matakana Island, now the most successful nesting area for the waders in the country. During the 2004–05 breeding season 30 chicks were raised from 42 pairs of New Zealand dotterels, and banded dotterels from previous broods are turning up all round the Bay of Plenty and nesting in new areas. Other birds, such as variable oystercatchers, are also benefiting from the absence of the predatory gulls, with many more chicks fledging than before. White-fronted terns have left the harbour and are now nesting on Mayor Island.
Predation by Larus dominicanus is well documented in other parts of the world. At Península Valdés, in Argentina, the gulls are increasingly feeding on skin and blubber that they gouge from the backs of southern right whales. Harassment of right whales was nearly five times more prevalent in 1995 than when first studied in 1984.
Black-backed gulls vary in their habits from place to place, however, and in some areas have been seen to coexist for long periods with other birds. Ray Clough has been watching birds for many years, especially in the Auckland area.
“I’ve seen several black-backed gulls cooperate to take ducklings of paradise ducks,” he recalls. “The ducklings dive at any sign of danger and somehow the gulls manage to grab them the instant they re-surface, while they are disoriented. But, while I’ve certainly seen gulls take weaker chicks and stragglers from a variety of species, I’ve never seen gulls wipe out a colony of other birds. On Rat Island, off Shelly Beach in the Kaipara, black-backed gulls essentially nested in a ring around a colony of white-fronted terns without destroying it, although they would have taken some chicks. At Sand Island, off Port Waikato, where there are thousands of nesting birds, especially black-backed gulls and Caspian terns, feathers are common in the pellets the gulls regurgitate, but the different species seem to coexist in quite a stable manner. Elsewhere, I’ve seen black-backs attack and eat sick wrybills, but not healthy individuals. I think that the gulls don’t deserve all the bad press they are inclined to get.”
It was estimated that there were 27,000 black-backed gulls in the Auckland city area in 1972. That was probably their peak year. Many bred on Rangitoto Island, where there were seven main colonies and several more dispersed breeding areas, all on bare (and inaccessible) lava fields. Robert Oliver, a master’s student in zoology, made a study of these gulls in the early 1970s.
Why were gulls so abundant on Rangitoto and why did they decline after 1972? From 1923 until the end of 1971, the Auckland Harbour Board dumped ships’ rubbish daily in the sea to the north of the island. In August 1971, Oliver estimated that 1500 gulls were feeding on this rubbish every day, which had greatly increased in quantity during the 1960s. However, from the beginning of 1972, ships’ rubbish was incinerated. Also during the 1960s, large open rubbish dumps had proliferated in the Auckland area, and some 10,000 black-backed gulls foraged daily in these. Largest were the tips at Barrys Point, on the North Shore (with an estimated 3000 birds), and at Galway Street, Onehunga (with about 5000 birds). Many gulls would also rest and forage on mudflats adjacent to these sites, and there were some 1000 birds on Lake Pupuke and 1000 more on the roof of the Challenge phosphate plant in the Penrose area. However, in November 1971 Devonport Borough Council introduced the compulsory use of plastic bags for household rubbish—the beginning of the end for the domestic rubbish tin. Other councils followed suit, and suddenly the vast quantities of discarded food at the tips was no longer so accessible.
This had an immediate affect on the black-backed gulls. In 1972, Oliver noticed that the number of nests on Rangitoto Island was down by 15 per cent on the year before, that eggs were smaller in size, and that fewer hatched. In 1971, 68–80 per cent of eggs hatched (depending on the colony), whereas in 1972 chicks emerged from only 64–68 per cent of eggs. Whereas more than 90 per cent of chicks fledged in 1971, only 73–86 per cent did so in 1972. Following further improvements in rubbish handling, gulls are no longer abundant at landfills, and numbers of the birds around Auckland have plummeted.
Oliver followed the annual cycle of the gulls on Rangitoto in some detail. Once breeding was complete in midsummer, the gulls forsook their island breeding grounds and spent March, April and May feeding around rubbish dumps to regain condition. They started to return to their breeding areas in June, and the first matings took place in early July. Oliver noticed that the birds became more attached to their breeding territories as the season progressed. If he approached a colony in July, all the birds would lift off. In November, no bird would move until he had got to within 2 or 3 m.
Egg-laying was at its peak from mid-October to November 22, and most chicks had hatched by December 17. Chicks were brooded by adults for just 3–6 days after the last egg had hatched and would start to wander from the nest after 5–10 days. Brooding habits on Rangitoto, and possibly also chick wandering, were at least partly influenced by the birds’ needing shade for relief from the heat reflected by the black lava fields.
Worms, household scraps, offal and small fish were the main items fed to chicks, and the youngsters would grow to 500–600 g on this enticing diet in about 20 days. By seven weeks of age chicks could fly, and they would start to leave the colony in mid-January, though the last would not depart until mid-April.
If chicks younger than eight days fetched up at the wrong nest, the adults there would usually accept them. Adult gulls seemed unable to distinguish between their own and others’ offspring at this stage, although Oliver found evidence that suggested chicks knew when they were not with their parents, having apparently learned to recognise parental calls while still in the egg. Straying chicks older than eight days were recognised as interlopers and often killed by adults.
The gulls appeared to be creatures of habit. Of eight pairs Oliver monitored, five or six bred again with the same mates the following year, and 80 per cent of birds returned to the nest site of the previous year. An earlier study on Somes Island had found that fighting between adults on the breeding ground was a significant cause of death. On Rangitoto there was plenty of room in which to nest and little squabbling. The main cause of death among adult birds was misadventure—for example, getting a foot or wing caught down a crack in the lava.
But there are more dramatic ways for black-backed gulls to perish. In the mid-1990s, an aircraft taking off from Wellington airport ingested a couple of black-backed gulls near the northern tip of the runway. Such large birds can do considerable damage to an aircraft engine. In this case the engine was disabled but the plane landed safely and no one was seriously injured. But the incident prompted the airport authorities to re-evaluate their gull-control measures. They hired WMIL to formulate and carry out a more aggressive gull-management plan. In its early years, this involved pricking eggs and culling adult birds in breeding hot spots around the region. In a controversial step, a breeding colony on Moa Point—an island just off the south-end of the airport—was completely removed, since that was where contact between gulls and planes was most likely.
Jason Graham, Airside Operations Coordinator at Wellington airport, says: “Bird culling was only carried out for a season or so in specifically identified areas. During the 2001–02 nesting season, we noticed that the bird numbers were lower than expected on [nearby] Taputeranga Island and around the Miramar Peninsula, so we discontinued the egg-pricking programme everywhere except Matiu/Somes and [adjacent] Mokopuna Islands.”
A number of factors have contributed to the fall in the region’s black-backed gull population to today’s estimated 5000–7500 birds. Several large-scale sewage and storm-water-drainage projects were completed in the late 1990s, severely inhibiting the gulls’ scavenging habits, while better street-cleaning and rubbish-collection held alternative food sources in check. Improved management and gull-control activities at a number of landfills in the region have also served to cut gull numbers. As in Auckland, open and uncontrolled landfills used to be quite common in the Wellington area, and the gulls prospered accordingly. Most landfills in the region are now better monitored and frequently covered, diminishing the gulls’ scavenging prospects.
Several tips also hire gull-control specialists who employ techniques to scare the birds away and sometimes cull them. But gulls are intelligent creatures: who hasn’t seen one carry a tuatua aloft and drop it on rocks to split it open? Control specialists find they need to frequently modify their scare tactics to remain effective. One gull-control worker who showed up at a tip in the same vehicle week after week eventually discovered the scavenging gulls would temporarily leave the area every time they saw his van, or another like it, approaching—only to return once he had departed. While gull numbers at most tips around Wellington are down, counts from 2003–04 show there is still room for improvement. For example, according to WMIL’s surveys, Porirua’s landfill still provides foraging for upwards of 2000 black-backed gulls.
“Beyond the risk to air traffic, that many gulls congregating at a tip can cause other health and safety concerns,” says Biz Bell. “Gulls carry a lot of diseases that pose a threat to other wildlife, as well as domestic animals and humans. Having a large flock of gulls scavenging at a landfill, and then roosting on nearby farmlands or playing fields, is not a good situation.”
Another prong of the airport’s gull-management plan included entering into a funded sponsorship agreement with DOC in 1997. The aim of this was slowly to reduce the gull population on Somes and Mokupuna Islands by more than half, to 400 nesting pairs. Since most of New Zealand’s southern black-backed gulls do not migrate, such a reduction would have year-round implications. To achieve it, an egg-pricking programme was started. The airport also began contributing financially to a native revegetation scheme on Somes Island initiated in 1981 by Lower Hutt Forest and Bird and the Ministry for Agriculture and Forestry. On the island, black-backed gulls prefer to nest in open grassy areas and on rock stacks—sites with good visibility. Wellington airport and DOC both saw restoring native vegetation as a long-term solution to controlling the gull population.
In late November 2004, I joined DOC gull-control contractors Reg Cotter and Maria Bogers on Somes Island to learn more about egg-pricking first-hand. Reg has been involved with the programme for five years, Maria for two. They met while working on a research project in the Chatham Islands five years ago. They operate well as a team, and as Reg says, “We’re out here for a week together, so it’s important to have good company.”
Forty-one-year-old Maria casually rolls a cigarette while enjoying morning tea. She works in insurance when she’s not in the field engaged on some DOC or university project. Her sturdy build and blonde dreadlocks seem at odds with work behind a desk, but on the island she looks right at home. She’s worked as a possum trapper for a private company and has trapped rats for various research projects. When she confesses to me that she was something of a tomboy as a kid, I can’t even feign surprise.
For his part, Reg has had a love affair with islands and birds since he was a youngster. Before he retired he worked in sales, but weekends and holidays were frequently spent doing voluntary work—bird counts, ornithological research projects, re-vegetation, clean-ups. Now in his mid-seventies (he’s a bit cagey when I ask how old he is), he labours tirelessly on conservation projects on Mana, Makaro/Ward (also in Wellington Harbour) and Somes Islands and in the Chatham Islands.
“I started doing bird counts 35 years ago on Matiu/Somes,” he says. “I think because the public wasn’t allowed on this island for so long [it opened to the public in 1995] it always held an extra attraction for me.”
We talk for a few moments, but both contractors are anxious to get back to work. With spring weather being so unpredictable, the two plan what they’re going to do each morning around wind speed and direction. We strike out for a protected area on the south side of the island. Trudging through the bush we find a gull’s nest relatively quickly. Reg pulls out a small instrument that looks like a water pistol containing blue liquid with a needle at the front. He pushes the needle gently into each of three eggs in the nest. Maria pulls out a bottle of burgundy-coloured fingernail polish and carefully paints an X on each shell. Reg fishes a small field book and pencil from his pack and notes the nest’s location and number of eggs.
The blue liquid is formaldehyde with dye added. “Just so people who might collect the eggs for eating will see they’ve been contaminated,” says Maria. “We mark them for the same reason, but also so we don’t do any nests twice.”
Leaving the pricked eggs in place should encourage the gulls to continue tending them and not reproduce again this season. If the eggs were removed, the gulls would certainly lay more.
In a few nests there are only one or two eggs. Since a clutch of three is typical, the female is likely to return to lay more.
We slowly descend to the beach. Reg hops agilely from rock to rock. Although nearly as old as Maria and me combined, he could leave us for dust. Yet he waits patiently for us and offers encouragement whenever the going gets tricky.
The pair take turns with the different jobs—prick, paint and log. The gulls shriek above as we pause at each nest, but only one swoops down in an effort to drive us away. Reg and Maria are attacked pretty regularly. The work isn’t for the fainthearted, and I’m keenly aware of the fear du Maurier and Hitchcock played on in The Birds.
The eggs are green-blue or buff, with purple or brown blotches—similar to those of the variable oystercatchers that also frequent the island. Oystercatcher eggs are smaller, though, and their nests mere scrapes in the sand—an effective camouflage against flying predators. Gull nests—built by the males—are more solidly constructed and sited on rock outcrops or among scrubby vegetation further from the shore.
When we come upon a nest with chicks, we marvel for a moment before moving on.
Hatched or pipping chicks we leave unharmed. During the several hours I’m with Maria and Reg we find 14 gull nests. Over the course of their five days on Somes Island this year, they will prick 800 eggs in 350 nests. In 1997, over the same length of time, contractors perforated 2300 eggs in 935 nests. It’s important to note that they don’t hit every nest—many on the rock stacks and steep grassy slopes cannot be reached, and still others go undetected.
At one point I bluntly ask Reg why he does this work. After all, there are quite a few people who are against the gull-control programme and many of them happen to be members of the various conservation organisations to which he belongs. He reminds me that numbers of black-backed gulls have ballooned as a direct result of human activities and he feels that bringing them under control is environmentally sensible. And, as a doer by nature, he wonders how he’d feel if there were an air accident caused by gull strike and he hadn’t done his bit.
With counts by contractors and volunteers, DOC staff figure they are close to the target number set for Wellington airport in 1997. Still, because black-backed gulls begin breeding at age four and have an average life expectancy of 14 years, continuing the egg-pricking programme may be the only way to keep them in check.
Determining an appropriate number of gulls on Somes Island for conservation purposes is a trickier matter. Monitoring the populations of other birds and wildlife on the island gives the best indication, but that’s a time-consuming business. Even with the lower population, Somes Island is the main breeding site in Wellington Harbour. As Biz Bell notes, “No one involved in the programme likes killing the gulls.” By the same token, she’s encouraged by her recent bird counts on Taputeranga Island, where the number of nesting variable oystercatchers has doubled and two pairs of reef herons are now nesting—a first for the programme. She attributes the breeding success of these other birds, in part at least, to the smaller gull population on Taputeranga.
Some weeks after my morning with Maria and Reg, I return to Somes Island. I’ve brought my kids and a blanket for a picnic at the top of the island. Numerous breeding pairs of black-backed gulls fervently rebuke us as we pass by their sterile nests. I can’t escape the thought that the painted X on each egg is a pitiless deception. Yet I’m amazed at the number of young gulls I see. I ask DOC ranger David Moss about the fledglings. He gets that glint in his eye, the same one he gets when asked about the chicken bones, and replies, “Yes, well quite a few of the birds abandoned their first nests after the pricking programme and successfully laid second clutches.”
So much for tending lifeless eggs. It looks as if whoever coined the term “bird-brained” must have been gulled!